it's indeed very very annoying if you can hear the music but just some bits of 'noise' from the other person's (in this case, yours) earphones,
i agree with
RustygrabenRe: An interesting experience in train.
Closed headphones should be subsidised by the government as part of its pollution-reduction effort. Earcups provide better isolation and comfort both for the listener and people in the vicinity. It is a win-win situation, really.

win win win!!
or turn the vol a bit lower...